Contactless radio frequency identification (RFID) systems typically include at least one reader and a plurality of transponders, which are commonly termed credentials, cards, tags or the like. The transponder may be an active or passive radio frequency communication device which is directly attached to or embedded in an article to be identified or otherwise characterized by the reader. Alternatively, the transponder may be embedded in a portable substrate, such as a card or tag, carried by a person to be identified or otherwise characterized by the reader.
Communication between the reader and transponder is enabled by cooperative resident circuits which are provided in each reader and transponder. The resident circuit of a reader typically includes an inductor and a capacitor. The capacitor is coupled in series between the inductor and a signal driver. The inductor is usually in the form of an antenna coil which is capable of magnetically coupling to an inductor in the resonant circuit of a compatible transponder through mutual inductance. The communication is initiated when a transponder is proximately positioned relative to the reader. The reader has a power supply which conveys a current to the reader resident circuit, causing the reader antenna to produce an excitation signal in the form of an electromagnetic field. The excitation signal couples to the antenna of the proximately positioned transponder through mutual inductance and the excitation signal powers and clocks the transponder circuitry initiating operation of the transponder. These components are typically mounted on a board, such as a printed circuit board.
The transponder operation comprises the generation of a response signal at a specified frequency and transmission of the resulting transponder's response signal back to the reader. In particular, the transponder resonant circuit receives a current and responds to the excitation signal which causes the transponder antenna to produce a response signal in the form of an electromagnetic field. The response signal couples to the reader antenna through mutual inductance in substantially the same manner as described above with respect to coupling of the excitation signal to the transponder antenna.
An important operating parameter of the reader is the range of the reader when communicating with a transponder. The range of a reader is inter alia strongly affected by the strength of the electromagnetic field generated by the reader resonant circuit. In order to generate a field strength which provides the reader with adequate range, the designer of the reader must properly specify a resonant circuit that is appropriately tuned to a predetermined frequency for the desired application of the RFID system. The range of the reader is often altered by characteristics of the operating environment in which the reader resides. In a typical case where the reader is mounted in a fixed location on a support structure, the range of the reader is susceptible to the materials of the mounting location and other objects within the operating environment. For example, if the mounting location of a reader is in an operating environment which includes nearby metal, the metal can de-tune the resonant circuit of the reader from the predetermined frequency and drastically reduce the range of the reader. For these reasons, it is often desirable to pot a reader in a plastic housing with an epoxy and mount the reader to a wall, away from metal objects. While this approach is desirable from a functional standpoint, it is often undesirable from an aesthetic standpoint as the housing provides an unacceptable finished look. For example, the reader housing protrudes from the surface of a wall an unacceptable distance and/or utilizes a cover plate designed solely for the reader but which may not aesthetically match the cover plates used throughout the building and particularly nearby space. Additionally, because the reader is potted in the plastic housing, the housing cannot be changed.